The invention relates to an antenna design improving the immunity of the antenna against detuning due to the users way of holding a terminal in which the antenna is implemented.
With the introduction of internal antennas in cellular phones, problems concerning detuning the antennas during talk have arised. This is due to the fact that the fingers of the user partly cover the antenna due to an inappropiate way of holding the phone. It has been tried to overcome these problems by designing the phone housing is a way so the user is invited to hold his fingers in an appropriate way.
An object of the invention is to provide an antenna including a PIFA structure having a ground plane element, at least one radiating element, and feeding means for connecting an RF connection to said at least one radiating element. The antenna furthermore comprises a conducting plate element arranged to be substantially in parallel with said PIFA structure, and said conducting plate element is electrically floating in relation to said at least one radiating element. The floating plate covers provides a shield for the antenna against the users fingers.
The conducting plate element is placed very close to the radiating element compared with the distance between the ground plane element and said at least one radiating element. The ratio of distance between the ground plane element and said at least one radiating element, and the distance between the conducting plate element and said at least one radiating element is preferably within the range two to eightxe2x80x94approximately four.
The size of the conducting plate element is substantially the same as the size of said at least one radiating element, and it exceeds the edges of said at least one radiating elementxe2x80x94at least along edge carrying significant edge currents. According to the preferred embodiment the edges of the conducting plate element exceeds the edges of said at least one radiating element along its entire periphery.
According to a second aspect of the invention there is provided a communication terminal for radio communication having an antenna, and including a PIFA structure being provided with a ground plane element, at least one radiating element, and feeding means for connecting a signal path from a transceiver of the terminal to said at least one radiating element. The antenna furthermore comprises a conducting plate element arranged to be substantially in parallel with said PIFA structure, and said conducting plate element is electrically floating in relation to said at least one radiating element. The floating plate protects the antenna from detuning when the user places his fingers close to the PIFA structure.
According to the preferred embodiment of the invention, the ground plane element is provided on a printed circuit board of the terminal, e.g. as a lid of shielding cans containing electric components, and said at least one radiating element is mounted on a dielectric body being mounted onto printed circuit board. The ground plane element and said at least one radiating element may be separated by an air gab. Preferably, the conducting plate element is mounted on a housing wall of the terminal as a metallic layer coated onto the inner housing wall. According to an alternative embodiment of the floating plate is constituted by a metal wall electrically floating in relation to the rest of the terminal.
According to a third aspect of the invention there is provided a method of reducing the detuning sensitivity of an antenna, including a PIFA structure being provided with a ground plane element, at least one radiating element, and feeding means for connecting a signal path from a transceiver of the terminal to said at least one radiating element. The method comprises placing a conducting plate element substantially in parallel with said PIFA structure, and allowing said conducting plate element to be electrically floating in relation to said at least one radiating element.